A. Field of the Invention
This invention relates to the field of bladders for cushions which contain flowable cushioning medium. More particularly, this invention relates to a bladder for a cushion, the bladder containing flowable cushioning medium, and the bladder having spot welds which are through-sewn to a base which is smaller in surface area than the bladder itself.
B. The Background Art
There are many types of cushions in the prior art which contain flowable cushioning media. Such cushions, if designed correctly, have the excellent properties of overall pressure reduction and pressure equalization across the cushion. This is achieved because the flowable medium, which is always contained in one or more bladders, flows under the cushioning pressure to reshape itself to the object being cushioned. This creates a greater total surface area being cushioned (to reduce overall pressure) and equalizes pressure across the cushioned object's surface (reducing or eliminating pressure peaks at protruding portions of the cushioned object).
In all effective prior art cushions which contain flowable media, the bladder which contains the media is oversized such that it is only filled to a portion of its capacity. This results in loose bladder skin, allowing the pliable bladder to move with the flowing media in conforming to the cushioned object. Bladders that do not have loose skin prevent the media from freely reshaping, thus harming the cushioning capability of the cushion.
The typical prior art means of achieving loose skin is as follows. A flat bladder is created by welding plastic films together around the edge of the bladder (edge weld) and at certain locations within the interior of the flat bladder (spot welds). The bladder is filled to partial capacity with a fluid material and the fill port is sealed. The bladder is then "scrunched up" (i.e. compacted by creating random folds and creases on the bladder surface) by (1) adhering portions of it via hook and loop to a base which is smaller than the fully extended partially filled bladder; (2) stuffing the bladder into an open-faced cavity which is smaller than the fully extended partially filled bladder; or (3) a combination of 1 and 2. By constraining the bladder into an area which is smaller than the fully extended size, the bladder skin becomes wrinkled and loose. The problem with (1) is that hook and loop can too easily separate, or the hook or loop side can loose its adherence to the plastic film, and is thus not secure. Further, hook and loop is expensive both to procure and to apply. Even further, the user of the cushion may become confused when reassembling the cushion, and assemble it with the wrong hook areas attached to certain loop areas, etc., or may not center the hook areas on the loop areas properly, resulting in a cushion which is sloppy in appearance or has lost some of its functionality. The problem with (2) above is that the tray adds to the expense of the cushion. Further, any cavity rigid enough to contain the bladder under the cushioning pressure creates the risk of contacting the object being cushioned and creating pressure peaks. To prevent this contact, the cushioned object (e.g., a person) must be located in a precise location, and is not free to move or be moved around. This reduces the desirability of a cushion, particularly to a person that desires to move around on the cushion. Further, the cavity adds weight to the cushion. Still further, it is difficult to control the location of various parts of the bladder relative to various parts of the cavity, and a cushion with sloppy appearance is created.
Another method for obtaining loose skin is described and claimed in my co-pending U.S. patent application Ser. No. 08/149,224, now U.S. Pat. No. 5,592,706, which is hereby incorporated by reference in its entirety. In brief, this includes the use of an elastomeric bladder which may be filled about 33% full with a flowable cushioning medium, although the bladder could be filled 10% to 95% of its volumetric capacity with flowable cushioning medium. A flowable cushioning medium used with that invention consists of lightly lubricated microspheres. This method of obtaining a loose bladder skin has the problems mentioned above related to hook and loop, or in the case of our current design, which puts individual bladders into a complex multi-cell fabric enclosure, adds substantial cost due to the sewing of the complex fabric. In any event, the use of many small bladders as opposed to one large bladder adds a great deal of cost because each bladder must be welded, trimmed, filled, and sealed.
Another prior art method for obtaining loose skin is described in U.S. Pat. Nos. 5,201,780 and 5,255,404, each of which is hereby incorporated by reference in its entirety. This method includes a large flat bladder segmented by welds, each segment being filled to partial capacity with a fluid. The bladder is stuffed into crevices in a piece of foam that is smaller than the fully-extended but partially filled bladder, which results in desirable wrinkles and loose skin (i.e. random folding and creasing of the bladder skin). The problem with this method is that the fluid is constrained to stay in each segment and cannot freely flow throughout the cushion, thus limiting the degree of shaping of the cushion to conform to the shape of the cushioned object, and of the opportunity for the cushioned object to sinking into the cushion. The problem with this method is solved with the invention disclosed in U.S. patent application Ser. No. 08/149,224, now U.S. Pat. No. 5,592,706, by using cells of various sizes to pre-shape the cushion. The users of the method of the '780 and '404 patents try to compensate for its deficiencies by placing each segment atop a piece of foam, which allows more deformation than would be permitted without the foam. However, this is labor-intensive and does not result in a reliable product because the adhesive or hook and loop means used to locate each segment could separate. Another problem with this method is that the foam will break down over time, reducing the effectiveness of the cushion and making the cushion appear sloppier.
Another method of obtaining loose skin in fluid-filled cushion bladders is to mold the bladders in three dimensions instead of using flat bladders. For examples of this, the reader is directed to U.S. Pat. Nos. 5,163,196, 5,052,068, 4,698,864, 5,111,544, 5,369,828, 4,713,854, and 3,605,145, each of which is incorporated by reference herein in its entirety. Such molding, vacuum forming, or pressure forming, however, is significantly more expensive than welding of flat films as in the other methods described above.
Accordingly, due to the various deficiencies in the prior art there is a need for a cushion bladder which has any combination of the following features listed below.
Other art which the reader should be aware of includes U.S. Pat. Nos. 4,485,505, 4,572,174, 4,498,205, 4,483,029, 4,247,963, 4,255,404, 3,893,198, 3,605,145, 2,814,053, 1,261,475, 5,163,196, 5,052,068, 4,698,864, 5,111,544, 5,369,828, 5,190,504, 5,335,907, 4,952,190, 3,748,779, 4,744,564, 3,518,786, 4,256,304, 5,204,154, 5,201,780, 5,147,685, 5,100,712, 5,093,138, 5,079,787, 5,079,786, 5,074,620, 5,058,291, 5,018,790, 5,015,313, 4,953,313, 4,952,439, 4,842,330, 4,761,843, 4,728,551, 4,726,624, 4,709,431, 4,467,053, 4,660,238, 4,588,229, 4,255,202, 4,243,754, 4,252,910, 4,229,546, 4,144,658, 4,083,127, 4,038,762, 3,986,213, 3,968,530, 3,748,669, 3,552,044, 3,529,368, 3,407,406, 5,103,518, 5,020,176, 5,010,608, 4,945,588, 4,292,701, 4,472,847, 3,462,778, 4,628,557, 2,672,183, 1,228,783, 5,421,874, 3,459,179, 4,163,297, 4,737,998, 2,491,557, 2,655,369, 4,713,854, 5,255,404, and 4,959,059, each of which is hereby incorporated by reference in its entirety. This art relates generally to the field of cushions, cushioning medium or seats and may be helpful to the reader in understanding the status of the art before the invention was made.